South Dakota School of Mines and TechnologyStudents Use Simulation Technology to Improve Underground Mine Safety

[Vol.1] Historically, improper mine ventilation has caused major disruptions in mining operations and can endanger worker health and safety. This paper discusses research being performed by students at the South Dakota School of Mines and Technology to better understand ventilation in mines. The students used Software Cradle’s SC/Tetra CFD software to simulate the airflow inside the working areas of the mine. The following narrative interview highlights their achievements.

Using CFD to Better Understand Underground Mine Ventilation

The ventilation of an underground mine presents a significant challenge for mine engineers who must ensure the work environment in the mine is properly ventilated. Air flow and pressure throughout a mine cannot be seen. In addition, conducting physical tests inside the mine is usually not feasible in the majority of cases.

Traditionally, mine engineers have had to rely on one-dimensional empirical formulas and their experience to design ventilation systems for underground mines. The fluid dynamics in a mine is extremely complex and does not always lend itself to being modeled accurately in this way. The advent of three-dimensional simulation tools and high powered computing platforms have elevated CFD modeling to become an important area of research for mine engineering universities. Consistent with this, the Mine Ventilation Research Group at the South Dakota School of Mines and Technology found that CFD simulation can be an accurate method for assessing ventilation conditions in mines.

The group at the university is led by Dr. Purushotham Tukkaraja. The work has been funded through a research grant from the National Institute for Occupational Safety and Health (NIOSH) and has resulted in two published papers about using CFD to simulate block/panel cave mining ventilation. Two additional papers have been accepted for publication in the proceedings for the 16th North American Mine Ventilation Symposium.

“CFD has been a very useful tool for this group because simulating the ventilation of an underground block/panel cave mine, as it develops, is quite complicated. The porous media model, diffusion model, and chemical reaction model have been at the core of the group’s research.” - Dr. Purushotham Tukkaraja

Using CFD is a practical way for mining engineers to visualize and accurately determine mass flow rates, pressure losses, and gas diffusion throughout a mine.

Figure 1: A “Block Caving” Mine in Operation
(click to enlarge)

Figure 2: 2D Block Cave Model (click to enlarge)

Block Cave Mining

Block cave mining is an underground mining technique that is more cost effective and productive than traditional open pit mining methods. This technique involves cutting two sets of tunnels, one directly on top of the other, underneath the orebody, which is located deep within the earth. The lower level tunnels are used as the extraction site (also called the production level). The upper level tunnels (undercut level) are used as a drilling site where explosives are detonated to break up the rock and initiate caving. Once the explosives are detonated, the rock fractures into smaller pieces. Vertical drilling at the draw points help encourage the broken rock to begin to crumble and fall. The material can then be continuously removed. As the ore is removed, gravity causes more rock to fracture, break up, and fall into the draw points. When this process is performed properly, the rock will continuously cave under its own weight, producing a continuous flow of ore to the draw points.

As the rock caves, an air gap grows between the broken rock region and the zone above where the rock has not yet caved. Using special equipment, miners continually monitor the air gap because if it becomes too large it could collapse violently. This could cause an air blast which could kill or injure workers. By using the monitoring device to assess the rate of caving versus the rate of production, mine engineers can maintain control of the air gap size. From a ventilation stand point, Dr. Tukkaraja’s group used CFD to determine an optimal air gap height to achieve adequate ventilation in the mine.

Another unseen hazard to the miners, in the case of extraction orebody with uranium mineralization, is the release of hazardous radon gas into the working environment. Radon is a tasteless, odorless, inert, radioactive, and likely carcinogenic gas. As the rock is broken, radon gas is released into the mine. To ensure the working environment is safe, the radon concentration in the working area must be diluted to a safe level. For block cave mining, engineers currently use empirical relationships to determine how much fresh air they need to supply to dilute radon concentrations to a safe working level. However, these relationships do not help engineers to know the actual radon concertation at different locations in the mine. Furthermore, studies have shown that these empirical relationships fail to estimate the amount of air that is required to dilute radon gas to a safe level.

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